This invention relates to a chimeric biotin-binding papillomavirus protein.
Papillomavirus are causative agents for several types of epithelial and mucosal diseases. Of particular concern is that certain strains of papillomavirus are associated with genital cancers, cancers of the head and neck, and also rectal cancers (see, e.g., Iwasawa et al., J. Urol., 149, 59-63 (1993); Koutsky et al., N. Engl. J. Med., 327, 1272-78 (1992)). Considerable efforts, therefore, are underway to prevent the spread of this virus by developing a prophylactic vaccine and novel treatments for papillomavirus-induced lesions (see, e.g., Cason et al., Vaccine, 11, 603-11 (1993); Crawford, Cancer Suev., 16, 215-29 (1993), Schiller et al., in Papillomavirus-Like Particles: Basic and Applied Studies (Lacey, C., ed., 101-12 (Leeds Medical Information, Leeds, U.K., 1996)).
Papillomaviruses are nonenveloped double-stranded DNA viruses about 55 nm in diameter with an approximately 8-kb genome in a nucleohistone core (Baker et al., Biophys J. 60, 1445-56 (1991)). The capsids include two viral proteins (L1 and L2) of about 55 kDa and 75 kDa, respectively (Larson et al., J. Virol., 61, 3596-3601 (1987)). L1 is the major capsid protein, and it is arranged in 72 pentameres within the capsid. In fact, L1 has the ability to self-assemble into virus-like particles (VLPs) upon production of the L1 protein in eukaryotic cells (see, e.g., Hagensee et al., J. Virol., 67, 315-22 (1993); Kirnbauer et al., J. Virol., 67, 6929-36 (1993)). The function and position of L2 within the virion are not clear, although the protein is assembled with L1 into VLPs when coexpressed in cells. The ratio of L1 to L2 within VLPs is about 30:1 (Kirnbauer et al., J. Virol., 67, 6929-36 (1993)).
VLPs typically are used for in vitro studies of papillomavirus infection, as opposed to intact papillomavirus (see, e.g., Roden et al., J. Virol., 68, 7260-66 (1994); Volpers et al., J. Virol., 69, 3258-64 (1995)), because of the lack of a suitable in vitro culture system. While it has been suggested that VLPs may prove useful as vectors for targeting drugs, nucleic acids, or other substances to cells subject to papillomavirus infection, they have not proven useful as a vector system. Recently, it has been discovered that chimeric fusion proteins consisting of the amino-terminal portion of the L1 or L2 protein fused to a portion of a non-structural papillomavirus protein are able to assemble into capsomeres and VLPs. VLPs including such chimeric molecules have been demonstrated to elicit an immune response from cells (see, e.g., published international application WO 96/11274; Mxc3xcller et al., Virology, 234, 93-111 (1997); Greenstone et al., Proc. Nat. Acad. Sci. (USA), 95, 1800-05 (1998)). While it is thus possible to use such chimeric capsomeres or VLPs for delivering the non-L1 or L2 portion of such fusion proteins to cells (e.g., as vaccines), the method is of limited utility. For example, such a method does not permit the delivery of nucleic acids or other non-proteinaceous species to cells. Moreover, such a method requires the engineering of a novel chimeric capsid protein for each desired application. In view of the foregoing problems, there exists a need for a vector system able to deliver a wide variety of substances to cells subject to papillomavirus infection.
The present invention provides a chimeric protein including a first domain which includes at least a portion of a papillomavirus L1 or L2 protein and a second domain which includes a biotin-binding polypeptide. The invention also provides papillomaviruses, capsomeres, and VLPs including such chimeric proteins and a method for delivering biotinylated substances to cells using such reagents. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the following detailed description.
The first domain of the chimeric protein includes at least a portion of a papillomavirus L1 or L2 protein. The sequence of the L1 and L2 proteins of many papillomaviruses is known, and the chimeric protein can include all or a portion of the L1 or L2 protein from any papillomavirus strain. The second domain includes a biotin-binding polypeptide, and it can be derived from any protein known to bind biotin, many of which are known in the art (see, e.g., Green et al., Meth. Enzymol., 184, 51-67 (1990); Howard et al., Gene, 35, 321-31 (1985); Li et al., J. Biol. Chem., 267, 855-63 (1992); Saggio et al., Biochem. J., 293, 613-16 (1993); Hiller et al., Biochem. J., 278, 573-85 (1991)). Examples of proteins from which the biotin-binding domain of the inventive chimeric protein, thus, include avidin, streptavidin, biotin operon repressor and biotin holoenzyme synthase, biotin carboxylase, biotin-binding phage, and the like.
Each domain of the chimeric protein contributes its respective function to the chimeric protein of the present invention. Thus, an L1 domain is able to interact as a native L1 protein (i.e., with either native L1 proteins from the same strain as the chimeric protein is derived or with other chimeric proteins) to form papillomaviruses, capsomeres, or VLPs. The L1 protein can be further modified (e.g., by deleting the residue corresponding to Cys 428 of the wild-type HPV 16 protein) to render it more able to form capsomeres than VLPs. Such modification is preferable in some applications to ensure that the biotin-binding domain is exposed, rather than hidden in the internal region of a VLP. Depending on how the protein is produced, however, an L1 domain can represent wild-type L1 sequence to permit the resulting chimeric protein to assemble into whole papillomaviruses or VLPs. Moreover, an L1 domain includes sequences able to bind receptors present on target cell surfaces. To provide these functions, where the chimeric protein includes an L1 domain, typically it includes at least the amino-terminal portion of the L1 protein. Similarly, where the chimeric protein includes an L2 domain, the L2 domain permits the chimeric protein to be incorporated into VLPs (see, e.g., WO 96/11274; Greenstone et al., supra). Similarly, the domain derived from a biotin-binding protein function as a ligand for biotin, thereby conferring biotin-binding ability to the chimeric protein of the present invention. Importantly, the biotin-binding domain should not be so large so as to inhibit the capsomere-, virus-, or VLP-forming ability of the L1- or L2-derived domain. Thus, where the chimeric protein includes a L1 domain, preferably, the biotin-binding domain is smaller than about 50 amino acids (e.g., smaller than about 30 amino acids), such as about 20 amino acids or smaller. Where the chimeric protein includes an L2 domain, the biotin-binding domain can be (but need not be) somewhat larger, for example, smaller than about 150 amino acids (e.g., smaller than about 100 amino acids), such as about 75 amino acids or smaller.
Chimeric proteins of the present invention can be synthesized using standard direct peptide synthesizing techniques (see, e.g., Bodanszky, Principles of Peptide Synthesis (Springer-Verlag, Heidelberg: 1984)), such as via solid-phase synthesis (see, e.g., Merrifield, J. Am. Chem. Soc., 85, 2149-54 (1963); Barany et al., Int. J. Peptide Protein Res., 30, 705-739 (1987); and U.S. Pat. No. 5,424,398). Alternatively, such modified proteins can be chemically crosslinked, and a variety of cross-linking agents are known in the art and widely available (e.g., succinimidyl or maleimidyl cross-linkers). Methods for conjugating peptides and polyamines are also well-known in the art (see, e.g., Staros, Biochem., 21, 3990 (1982)). Alternatively, a DNA fragment encoding the chimeric protein can be subcloned into an appropriate vector using well known molecular genetic techniques. The fragment then is transcribed and the peptide subsequently translated in vitro within a host cell. Any appropriate expression vector (see, e.g., Pouwels et al., Cloning Vectors: A Labratory Manual (Elsevior, N.Y.: 1985)) and corresponding suitable host cells can be employed for production of recombinant peptides. Expression hosts include, but are not limited to, bacterial species, mammalian or insect host cell systems including baculovirus systems (e.g., as described by Luckow et al., Bio/Technology, 6, 47 (1988)), and established cell lines such 293, COS-7, C127, 3T3, CHO, HeLa, BHK, etc. From such cells, the modified chimeric proteins can be harvested by standard techniques.
As mentioned, by virtue of the L1- or L2-derived domain, the chimeric protein of the present invention preferably is able to be incorporated into papillomaviruses and VLPs. Thus, the present invention provides a papillomavirus or VLP including at least one chimeric protein such as previously described. Preferably, a majority of the L1 or L2 domains in the papillomavirus or VLP are contributed by such chimeric proteins, and it is most preferred for all of the L1 or L2 domains in the papillomavirus or VLP to be contributed by such chimeric proteins. Of course, a papillomavirus or VLP can include some native L1 and/or L2 proteins, or other derivatives of L1 or L2 proteins not binding biotin. By virtue of the biotin-binding domain present on the proteins, the papillomavirus or VLP is able to bind biotin with high affinity.
Because each domain of the chimeric protein contributes its respective function to the chimeric protein, where the chimeric protein includes an L1 domain, the protein is able to form a capsomere. Thus, the present invention provides such a capsomere including at least one chimeric protein such as previously described, particularly one having an L1 domain. Preferably, a majority of the proteins in the capsomere are such chimeric proteins, and it is most preferred for the capsomere to include only such chimeric proteins. By virtue of the biotin-binding domain present on the proteins, the capsomere is able to bind biotin with high affinity.
Capsomeres, papillomavirus, and VLPs including the inventive chimeric proteins can be produced by methods known in the art. Typical methods for producing capsomeres and VLPs involve the expression of at lest a gene encoding L1 proteins within a suitable host cell. Coexpression of the L2 protein permits the L2 protein to be included within the VLP. Once produced within the host cell, the gene products aggregate to form intact viruses, capsomeres, and/or VLPs, which are then isolated from the cell and purified (see, e.g., Mxc3xcller et al., Virology, 234, 93-111 (1997)). Such standard methods are equally applicable to papillomaviruses, capsomeres, and VLPs incorporating the chimeric proteins of the present invention. However, the presence of the biotin-binding domain affords an additional method of purifying such viruses, capsomeres and VLPs using a biotin in accordance with standard protocols (e.g., on an affinity column or other suitable support).
Because the L1- or L2-derived domains of the inventive chimeric proteins retain the ability to bind cellular receptors, viruses, capsomeres, and VLPs incorporating such chimeric proteins can be employed to deliver biotinylated substances to cells, particularly cells normally infected by papillomaviruses. Thus, an aspect of the present invention is a method for delivering a biotinylated compound to a cell. The method involves first forming a complex comprising the biotinylated substance and a papillomavirus, capsomere, or VLP including a chimeric protein as herein described. Subsequently, the complex is exposed to the cell under conditions sufficient for the complex to bind the cell.
The cell is any cell for which papillomaviruses are normally tropic. In this regard, the method can be employed to deliver the biotinylated substance to cells either in vitro or in vivo, depending on the desired application of the method. Cell binding is mediated, at least primarily, via by the ligand-substrate interaction between the L1 proteins (e.g., any native L1 proteins as well as chimeric proteins containing L1 domains) comprising the papillomavirus, capsomere, or VLP. Thus, the strain of papillomavirus from which the L1 domain of the chimeric protein is derived (or other L1 proteins or derivatives present in the complex) can be selected so as to target the biotinylated substance to a given cell type.
The method can be employed to deliver any desired substance to the cells of interest, provided that the substance can be biotinylated (e.g., conjugated to a biotin-like molecule). For example, the substance can include a protein, a polynucleic acid, a drug, etc. Some substances function as markers for identifying cells to which the complex has been delivered. Thus, for use as a vaccine, the substance can be or comprise a viral antigen (e.g., a papillomavirus E2 or E7 protein). In other applications, the substance can be or comprise a compound that exerts a biological effect on the infected cells. For example, because the complex is targeted to cells for which papillomaviruses exhibit tropism, the substance can exert a biological effect on papillomavirus-infected cells or cells subject to infection. Thus, for treating tumors (e.g., cervical or penile cancers), warts, or other papillomavirus-related lesions, the substance can be a medicament, cytotoxin, chemotherapeutic agent, radioactive agent, etc. In other embodiments, the substance can be a nucleic acid including a gene encoding a bioactive molecule. In such circumstances, the complex delivers the nucleic acid to the infected cells such that the cells internalize it and can express the gene to produce the bioactive molecule. For combating tumors associated with papillomavirus infection, such a gene can encode a cytokine (e.g., tumor necrosis factor (TNF), TGF-xcex1, TGF-xcex2, interleukins (IL) such as IL-1, L-2, IL-3, etc., GM-CSF, G-CSF, M-CSF, co-stimulatory factor B7, etc.), a protein that promotes cell death or an enzyme that converts a prodrug into a cytotoxin (e.g., HSV-tk, cytosine deaminase, xanthine/guanine phosphoribosyl transferase, cytochrome p450 2B1, etc.). In other applications, the gene can encode a viral antigen to function in an immunotherapeutic protocol (e.g., a papillomavirus E2 or E7 antigen). Still other bioactive molecules are RNA species having sequences antisense to portions of papillomavirus genes (e.g., the genes encoding L1, L2).
While many such substances for delivery to cells in accordance with the inventive method can be obtained commercially as biotinylated compounds, other substances not available as biotinylated preparations can be conjugated to biotin before use in the inventive method using standard techniques (see, e.g., Parmley et al., Gene, 73, 305-18 (1988)). Once biotinylated, the substance to be delivered to the cell is exposed to a papillomavirus, capsomere, or VLP including a chimeric protein under conditions for the two to form a complex. Such a complex is formed by virtue of the high affinity ligand-substrate interaction between the biotin-binding portion of the chimeric protein(s) comprising the papillomavirus, capsomere, or VLP. The stoichiometric ratio of the number of biotinylated substance particles to the capsomere or VLP will vary depending on the proportion of chimeric proteins of the type herein described within the papillomavirus, capsomere, or VLP. The interaction of biotin with its ligands is well-known, and the complex can be formed under any suitable condition which will permit such interaction.
In addition to including the biotinylated substance and the papillomavirus, capsomere, or VLP including a chimeric protein as herein described, the complex can also include other constituents (e.g., one or more proteins, polynucleic acids, lipids, drugs, etc.). For example, incorporating lipids into the complex (e.g., in the form of liposomes) enhances cellular uptake of many types of pharmacologically active agents, especially nucleic acids (see, e.g., Innes et al., J. Virol., 64, 957-61 (1990); Morishaita et al., Hypertension, 21, 894-99 (1993); U.S. Pat. No. 5,635,380). Where a liposome is employed in the complex, and where the biotinylated substance includes a polynucleic acid, preferably the liposome contains cationic lipids, but it can, of course, contain neutral lipids as well. Preferred cationic lipids include LIPOFECTIN (DOTMA) (Gibco BRL), LIPOFECTMINE (Gibco BRL), and DOTAP (Boeringer-Mannheim), and others are known in the art (see, e.g., U.S. Pat. No. 5,736,392).
Once formed, the complex is exposed to the cell under conditions sufficient for the complex to bind the cell. The biotinylated substance is thus brought into proximity to, and delivered to, the cell. In some instances, the substance is internalized into the cell, while in other instances, it remains in contact (either transiently or long-term) with the exterior of the cell where it exerts its effect.
As mentioned, the inventive method can be employed to deliver the substance to cells either in vivo or in vitro. To facilitate the application of the method in vivo, the invention provides a pharmaceutical composition comprising a complex as herein described and a pharmaceutically-acceptable carrier. Such compositions can be manufactured in a manner that is itself known, e.g., by means of conventional mixing, dissolving, granulating, dragee-making, levigating, emulsifying, encapsulating, entrapping or lyophilizing processes.
Pharmaceutical compositions for use in accordance with the present invention can be formulated in a conventional manner using one or more pharmacologically or physiologically acceptable carriers comprising excipients, as well as optional auxiliaries which facilitate processing of the active compounds into preparations which can be used pharmaceutically. Proper formulation is dependent upon the route of administration chosen. Thus, for injection, the active ingredient can be formulated in aqueous solutions, preferably in physiologically compatible buffers. For trausmucosal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are generally known in the art. For oral administration, the active ingredient can be combined with carriers suitable for inclusion into tablets, pills, dragees, capsules, liquids, gels, syrups, slurries, suspensions and the like. For administration by inhalation, the active ingredient is conveniently delivered in the form of an aerosol spray presentation from pressurized packs or a nebuliser, with the use of a suitable propellant. The active ingredient can be formulated for parenteral administration by injection, e.g., by bolus injection or continuous infusion. Such compositions can take such forms as suspensions, solutions or emulsions in oily or aqueous vehicles, and can contain formulatory agents such as suspending, stabilizing and/or dispersing agents. Other pharmacological excipients are known in the art.
While it is believed that one of skill in the art is fully able to practice the present invention after reading the foregoing detailed description, the following examples are set forth to further illustrate some of its features. In particular, these examples detail several chimeric proteins, each including a first domain which includes at least a portion of a papillomavirus L1 protein and a second domain which includes a biotin-binding polypeptide. The examples also demonstrate that such proteins can be employed as described above to deliver biotinylated substances to cells. As these examples are included for purely illustrative purposes, they should not be construed to limit the scope of the invention in any respect.
The procedures employed in these examples, such as vector construction (including DNA extraction, isolation, restriction digestion, ligation, sequencing etc.), PCR, cell culture (including antibiotic selection), transfection of cells, protein assays (Western blotting, immunoprecipitation, immunofluorescence, ELISA, Wehi assays, etc.), etc. are techniques routinely performed by those of skill in the art (see generally Sambrook et al., Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1989)). Accordingly, in the interest of brevity, such basic elementary experimental protocols are not discussed in detail.